In a number of machine tool applications, multiple operations must be performed successively on a fixed workpiece at the same location. For example, the assembly of the exterior skin of an airplane fuselage may require drilling a hole, inserting a rivet into the hole, upsetting the rivet, and shaving the rivet head. Automatic fastening machines for performing these operations are well known. Such a machine utilizes a controlled transfer head that selectively positions various tools carried by the machine for sequential operation on a workpiece. Typically, the different tools in the transfer head are arranged in linear fashion. The linear carriage enables the tools to be indexed in a straight line into a working position aligned with a work axis that is disposed substantially perpendicular to the plane of the workpiece. A control system moves the tools into and out of alignment with the work axis depending on the required sequence for the manufacturing operation that is being performed. It is common to have separate actuators or feed mechanisms for each tool. The separate feed mechanisms drive the tool toward the workpiece after it has been aligned by the indexing mechanism. Also, certain tools such as drills require drive mechanisms for rotating the tool. Accordingly, the number and different types of mechanisms associated with indexing, feeding and rotating the tools presents a drawback to the linear carriage type systems.
Another drawback to these type of systems is that it is difficult to retrofit the linear carriages of existing machines unless the existing machine has the same number of tool positions.
As an alternative to having independent feed mechanisms for each tool, a centralized feed mechanism capable of engaging with the individual tools can be provided. However, the feed mechanism should be direct coupled to the tools to prevent backlash or chatter, and therefore the single feed mechanism introduces complexity due to the fact that each tool has to be separately brought into alignment and engagement with the central feed mechanism.
There have been tool changers and other machine tool devices that dispose machine tools about a turret perpendicular to the axis of rotation of the turret such as the devices disclosed in U.S. Pat. Nos. 3,296,896; 3,975,109; and, 4,679,276. However, these patents generally disclose turrets designed specifically for cutting tools. The purpose of the turrets disclosed in these patents is to provide tool changers that separately and individually engage different cutting tools with a central drive. Accordingly, the systems include clutches and transmissions for engaging the tools and for driving the tools at different speeds. These systems suffer from some of the same drawbacks discussed above such as the complexity associated with having to separately and individually engage numerous tools with a central drive. Also, these patents address a different problem, namely using a single drive to rotate tools over wide ranges of speeds. Furthermore, none of the prior patents is suitable for use in riveting operations where forming forces can reach into the tens of thousands of pounds.
Accordingly, what is needed is an indexing turret head apparatus that is capable of indexing several tools into a single position relative to a workpiece, that has a single actuator device for all of the tools, that does not require separate engagement of the actuator device with the tools, and that is suitable for use with fastener installation tools for installing fasteners such as rivets where the forming forces for upsetting the rivet are typically in the range of tens of thousands of pounds.